1. Field of the invention
The present invention relates, in general, to novel photoresist compositions useful for fabrication processes for semiconductor devices and, more particularly, to novel photoresist compositions employing phosphazene compounds as ballast, unabsorbent of light at a band of i-line (wavelength 365 nm) and g-line (wavelength 436 nm) and superior in thermal resistance and sensitivity as well as resolution.
2. Description of the Prior Art
As high integration of semiconductor devices has been accelerated in the last few years, fine image-forming technologies useful for fabrication of semiconductor devices become highly precise. Correspondingly, photoresist used in the fine image-forming technologies is required to have a combination of high sensitivity, high resolution, and superior thermal resistance.
As a fine image-forming technology, there is extensively employed a lithography technology which takes advantage of a g-line with a wavelength of 436 nm and an i-line with a wavelength of 365 nm from a mercury lamp, a light source. In addition, there are various methods, what is called, next generation lithography technology, using an excimer laser (KrF, wavelength 248 nm), an X-ray and an electron beam.
Phenol novolak/naphthoquinone diazide-benzophenone resist compositions are widely used as photoresist for UV (g-line, i-line). In these resist compositions, benzophenone compounds serve as ballast and are exemplified by trihydroxy benzophenone (U.S. Pat. Nos. 3,666,473 and 4,115,128), tetrahydroxy benzophenone (Japanese Patent Laid-Open Publication Nos. Sho. 61-45240, Sho. 61-118744 and Sho. 62-280737) and so on. Herein, ballast means a kind of a latent compound which can function as a photosensitive agent through ether reaction of its photosensitive group, that is to say, a precursor compound having a photosensitive group.
However, since these exemplified compounds absorb light at a band of i-line which is most extensively used at present, the resulting photoresists are poor in transparency, which, in turn, deleteriously affect profile or resolution. In addition, the exemplified benzophenone compounds have low solubilities in resist solutions.